TRPV1 antagonists that cause hypothermia, instead of hyperthermia, in rodents: Compounds' pharmacological profiles, in vivo targets, thermoeffectors recruited and implications for drug development.

AIM: Thermoregulatory side effects hinder the development of transient receptor potential vanilloid-1 (TRPV1) antagonists as new painkillers. While many antagonists cause hyperthermia, a well-studied effect, some cause hypothermia. The mechanisms of this hypothermia are unknown and were studied herein. METHODS: Two hypothermia-inducing TRPV1 antagonists, the newly synthesized A-1165901 and the known AMG7905, were used in physiological experiments in rats and mice. Their pharmacological profiles against rat TRPV1 were studied in vitro. RESULTS: Administered peripherally, A-1165901 caused hypothermia in rats by either triggering tail-skin vasodilation (at thermoneutrality) or inhibiting thermogenesis (in the cold). A-1165901-induced hypothermia did not occur in rats with desensitized (by an intraperitoneal dose of the TRPV1 agonist resiniferatoxin) sensory abdominal nerves. The hypothermic responses to A-1165901 and AMG7905 (administered intragastrically or intraperitoneally) were absent in Trpv1-/- mice, even though both compounds evoked pronounced hypothermia in Trpv1+/+ mice. In vitro, both A-1165901 and AMG7905 potently potentiated TRPV1 activation by protons, while potently blocking channel activation by capsaicin. CONCLUSION: TRPV1 antagonists cause hypothermia by an on-target action: on TRPV1 channels on abdominal sensory nerves. These channels are tonically activated by protons and drive the reflectory inhibition of thermogenesis and tail-skin vasoconstriction. Those TRPV1 antagonists that cause hypothermia further inhibit these cold defences, thus decreasing body temperature. SIGNIFICANCE: TRPV1 antagonists (of capsaicin activation) are highly unusual in that they can cause both hyper- and hypothermia by modulating the same mechanism. For drug development, this means that both side effects can be dealt with simultaneously, by minimizing these compounds' interference with TRPV1 activation by protons.

A Monte Carlo-based model of gold nanoparticle radiosensitization accounting for increased radiobiological effectiveness.

Radiosensitization using gold nanoparticles (AuNPs) has been shown to vary widely with cell line, irradiation energy, AuNP size, concentration and intracellular localization. We developed a Monte Carlo-based AuNP radiosensitization predictive model (ARP), which takes into account the detailed energy deposition at the nano-scale. This model was compared to experimental cell survival and macroscopic dose enhancement predictions. PC-3 prostate cancer cell survival was characterized after irradiation using a 300 kVp photon source with and without AuNPs present in the cell culture media. Detailed Monte Carlo simulations were conducted, producing individual tracks of photoelectric products escaping AuNPs and energy deposition was scored in nano-scale voxels in a model cell nucleus. Cell survival in our predictive model was calculated by integrating the radiation induced lethal event density over the nucleus volume. Experimental AuNP radiosensitization was observed with a sensitizer enhancement ratio (SER) of 1.21 ± 0.13. SERs estimated using the ARP model and the macroscopic enhancement model were 1.20 ± 0.12 and 1.07 ± 0.10 respectively. In the hypothetical case of AuNPs localized within the nucleus, the ARP model predicted a SER of 1.29 ± 0.13, demonstrating the influence of AuNP intracellular localization on radiosensitization.

Effect of particle size on the lymphatic distribution of 111Indium-aminopolystyrene through intrapleural administration.

The study examined the impact of size on lymphatic particle distribution through intrapleural (ipl.) administration. Aminopolystyrene of three sizes, 0.29 microm, 2.18 microm, and 11.2 microm were radiolabeled with 111Indium and their biodistributions were evaluated in rats after ipl administration. Animals received either particles of three different sizes (4 mg, 200 microCi/animal) or unconjugated 111Indium as control. The percentage of injected dose (%ID) per organ or sample was determined for left (L) and right (R) mediastinal lymph nodes (LN), blood, lung, and pleural wash. The biodistribution of 2.18 microm 111In-aminopolystyrene was further investigated at 6 h, 24 h, 48 h, and 72 h following ipl administration to examine the possible particle retention time. The 2.18 microm particles had significantly higher uptake in both LLN and RLN compared to other sizes. The systemic uptake was minimal. At 72 h, there was still 3.2 +/- 3.2% and 2.1 +/- 1.8% of injected dose retained in the LLN and RLN, respectively. Scintigraphic imaging revealed significant accumulation of the radioactivity in mediastinal nodes. Particle size has significant impact on lymphatic particle distribution through ipl administration. Approximately 2 microm seems to be a suitable size.

A phase I study of 99mTc-hR3 (DiaCIM), a humanized immunoconjugate directed towards the epidermal growth factor receptor.

A phase I trial was conducted to evaluate the safety, tumour and normal tissue localization, pharmacokinetics and radiation dosimetry of Tc-hR3, a humanized monoclonal antibody directed towards the epidermal growth factor receptor, in 12 patients with recurrent or metastatic epithelial malignancies. Patients were injected intravenously with 3.0 mg or 6.0 mg (1010 MBq) of Tc-hR3. Blood and plasma concentrations of radioactivity were measured and a complete 24 h urine collection was obtained. Whole-body images were acquired up to 24 h post-injection and normal organ uptake quantified. Radiation dosimetry was estimated using MIRDose. Safety was evaluated by clinical observation, biochemical/haematological testing and by measuring immune response to Tc-hR3. There were no adverse effects, no changes in biochemical/haematological indices and no immune response to Tc-hR3. Tc-hR3 was rapidly cleared from the blood with a distribution half-life of 10.8+/-3.8 min. The volume of distribution, and clearance, were 180+/-37 ml.kg and 14+/-3 ml.kg.min, respectively. The elimination phase could not be discerned due to increasing blood radioactivity at later times. About 19-24% was excreted in the urine. Normal tissue uptake was mainly in the liver (44-50%), spleen (3-4%) and kidneys (3%). Imaging was positive in one patient with squamous cell carcinoma of the mouth and an involved cervical lymph node. The whole-body radiation dose from Tc-hR3 was 1.34+/-0.02x10 mSv.Bq. We conclude that Tc-hR3 exhibited an excellent safety profile. Future studies to determine the sensitivity and specificity of imaging with Tc-hR3 in a larger group of patients with pre-selection for epidermal growth factor receptor positivity are planned.

Amplified delivery of indium-111 to EGFR-positive human breast cancer cells.

A method is described to amplify the delivery of 111In to human breast cancer cells utilizing a novel human serum albumin-human EGF (HSA-hEGF) bioconjugate substituted preferentially in the HSA domain with multiple DTPA metal chelators for 111In. 111In-DTPA-HSA-hEGF exhibited a lower receptor-binding affinity than 111In-DTPA-hEGF but was rapidly and specifically bound, internalized and translocated to the nucleus in EGFR-positive MDA-MB-468 breast cancer cells. 111In-DTPA-HSA-hEGF was cytotoxic in vitro mainly through the emission of short-range Auger electrons and partially through the effects of the hEGF moiety to MDA-MB-468 cells overexpressing EGFR (1-2 x 10(6) receptors/cell) but not towards MCF-7 breast cancer cells with a 100-fold lower level of EGFR on their surface. The cytotoxicity in vitro against MDA-MB-468 cells of 111In-DTPA-HSA-hEGF substituted with nine DTPA chelators was enhanced 4-fold compared to 111In-DTPA-hEGF monosubstituted with DTPA. Studies are planned to further evaluate 111In-DTPA-HSA-hEGF in vivo as a new imaging and targeted radiotherapeutic agent for breast cancer.

Rapid imaging of human melanoma xenografts using an scFv fragment of the human monoclonal antibody H11 labelled with 111In.

H11 is a human IgM monoclonal antibody which recognizes a novel tumour-associated antigen expressed on melanoma, glioma, breast cancer, colon cancer, prostate cancer, lung cancer and B-cell lymphoma. In this study, a recombinant single-chain Fv (scFv) fragment of H11 labelled with 111In was investigated for tumour imaging in athymic mice implanted subcutaneously with A-375 human melanoma xenografts. H11 scFv was derivatized with diethylenetriaminepentaacetic acid (DTPA) for labelling with 111In. The immunoreactivity of DTPA-H11 scFv against A-375 cells in vitro ranged from 23% to 36%. 111In-DTPA-H11 scFv was rapidly eliminated from the blood and most normal tissues (except the kidneys) reaching maximum tumour/blood ratios of 12:1 at 48 h post-injection. Tumours were imaged as early as 40 min after injection. The kidneys accumulated the highest concentration of radioactivity (up to 185% injected dose/g). Tumour uptake was 1-3% injected dose/g. The whole-body radiation absorbed dose predicted for administration of 185 MBq of 111In-DTPA-H11 scFv to humans was 37 mSv. The radiation absorbed dose estimates for the kidneys, spleen and intestines were 405 mSv, 698 mSv and 412 mSv, respectively. The results of this preclinical study and a concurrent phase I trial suggest a promising role for H11 scFv for tumour imaging.

Abrogation of G2 checkpoint specifically sensitize p53 defective cells to cancer chemotherapeutic agents.

BACKGROUND: Chkl is a checkpoint gene that is activated after DNA damage. It phosphorylates and inactivates Cdc25C at the late G2 phase. The inactivation of Cdc25C and consequently, the inactivation of Cdc2, are required for the G2 arrest induced by DNA damage. METHODS: We treated 184B5 cell line and its E6 transformed cell lines with adriamycin in the presence of staurosporine or UCNO1 and examined G2 arrest and cell death. RESULTS: We found that adriamycin induced a p53 and p21 response as well as a G1 arrest in 184B5 cells, but not in its E6 transformed cells. Staurosporine or UCNO1 abrogated the G2 arrest induced by adriamycin in both cell lines. In addition, staurosporine or UCNO1 specifically sensitized p53 incompetent cells to adriamycin. CONCLUSION: G2/M checkpoint abrogators can potentially enhance the cytotoxic effect of conventional chemotherapeutic reagents specifically to tumor cells.

A comparison of EGF and MAb 528 labeled with 111In for imaging human breast cancer.

UNLABELLED: Our objective was to compare 111In-labeled human epidermal growth factor (hEGF), a 53-amino acid peptide with anti-epidermal growth factor receptor (EGFR) monoclonal antibody (MAb) 528 (IgG2a) for imaging EGFR-positive breast cancer. METHODS: hEGF and MAb 528 were derivatized with diethylenetriamine pentaacetic acid (DTPA) and labeled with 111In acetate. Receptor binding assays were conducted in vitro against MDA-MB-468 human breast cancer cells. Biodistribution and tumor imaging studies were conducted after intravenous injection of the radiopharmaceuticals in athymic mice bearing subcutaneous MCF-7, MDA-MB-231, or MDA-MB-468 human breast cancer xenografts or in severe combined immunodeficiency mice implanted with a breast cancer metastasis (JW-97 cells). MCF-7, MDA-MB-231, JW-97, and MDA-MB-468 cells expressed 1.5 x 10(4), 1.3 x 10(5), 2.7 x 10(5), and 1.3 x 106 EGFR/cell, respectively in vitro. RESULTS: 111In-DTPA-hEGF and 111In-DTPA-MAb 528 bound with high affinity to MDA-MB-468 cells (Ka of 7.5 x 10(8) and 1.2 x 10(8) L/mol, respectively). 111In-DTPA-hEGF was eliminated rapidly from the blood with < 0.2% injected dose/g (%ID/g) circulating at 72 h after injection, whereas 111In-DTPA-MAb 528 was cleared more slowly (3%ID/g in the blood at 72 h). Maximum localization of 111In-DTPA-hEGF in MDA-MB-468 tumors (2.2 %ID/g) was 10-fold lower than with 111In-DTPA-MAb 528 (21.6 %ID/g). There was high uptake in the liver and kidneys for both radiopharmaceuticals. Tumor-to-blood ratios were greater for 111In-labeled hEGF than for MAb 528 (12:1 versus 6:1), but all other tumor-to-normal tissue ratios were higher for MAb 528. MDA-MB-468 and JW-97 tumors were imaged successfully with both radiopharmaceuticals, but tumors were more easily visualized using 111In-labeled MAb 528. There was no direct quantitative relationship between EGFR expression on breast cancer cell lines in vitro, and tumor uptake of the radiopharmaceuticals in vivo, but control studies showed that tumor uptake was receptor mediated. CONCLUSION: Our results suggest that the tumor uptake in vivo of receptor-binding radiopharmaceuticals is controlled to a greater extent by their elimination rate from the blood than by the level of receptor expression on the cancer cells. Radiolabeled anti-EGFR MAbs would be more effective for tumor imaging in cancer patients than peptide-based radiopharmaceuticals such as hEGF, because they exhibit higher tumor uptake at only moderately lower tumor-to-blood ratios.

Pre-targeted radioimmunotherapy of human colon cancer xenografts in athymic mice using streptavidin-CC49 monoclonal antibody and 90Y-DOTA-biotin.

Radioimmunotherapy of solid malignancies using directly labelled 90Y-monoclonal antibodies has been associated in clinical trials with dose-limiting bone marrow toxicity. Our objective in this study was to evaluate the efficacy and toxicity of an alternative two-step pre-targeted radioimmunotherapy protocol for the treatment of human colon cancer. The two-step protocol consisted of administration of the tumour-associated glycoprotein (TAG-72) monoclonal antibody CC49 conjugated to streptavidin, followed by administration of 90Y-DOTA-biotin. Swiss nu/nu athymic mice bearing subcutaneous LS174T human colon cancer xenografts were injected intraperitoneally with streptavidin-CC49 (250 micrograms), followed 40 h later by an intravenous injection of 90Y-DOTA-biotin (900 microCi, 40 micrograms). Tumour growth was measured over 25 days and compared with that in control mice receiving no treatment. Bone marrow and normal tissue toxicity was determined by peripheral blood leucocyte counts and by monitoring the body weight of the animals. Pre-targeted radioimmunotherapy resulted in a modest (30-40%) decrease in the mean tumour growth rate in treated mice compared to control animals. There was no change in body weight following treatment and peripheral blood leucocyte counts remained within the normal range. Pre-targeted radioimmunotherapy was safe at administered amounts of 90Y radioactivity, which were at least nine-fold higher than those previously determined to be lethal using directly labelled 90Y-monoclonal antibodies. The results of this study are promising for the application of pre-targeted radioimmunotherapy using streptavidin-CC49 and 90Y-DOTA-biotin for the treatment of advanced colorectal cancer in humans.

111In-labeled EGF is selectively radiotoxic to human breast cancer cells overexpressing EGFR.

UNLABELLED: Our objective was to determine whether the internalization and nuclear translocation of human epidermal growth factor (hEGF) after binding to its cell surface receptor (EGFR) could be exploited to deliver the Auger electron emitter 111In into EGFR-positive breast cancer cells for targeted radiotherapy. METHODS: hEGF was derivatized with diethylenetriamine pentaacetic acid (DTPA) and radiolabeled with 111In-acetate. The internalization of 111In-DTPA-hEGF by MDA-MB-468 breast cancer cells (1.3x10(6) EGFRs/cell) was determined by displacement of surface-bound radioactivity by an acid wash. The radioactivity in the cell nucleus and chromatin, isolated by differential centrifugation, was measured. The effect on the growth rate of MDA-MB-468 or MCF-7 (1.5x10(4) EGFRs/cell) cells was determined after treatment in vitro with 111In-DTPA-hEGF, unlabeled DTPA-hEGF, or 111In-DTPA. The surviving fraction of MDA-MB-468 or MCF-7 cells treated in vitro with 111In-DTPA-hEGF was determined in a clonogenic assay. The radiotoxicity in vivo against normal hepatocytes or renal tubular cells was evaluated by measuring alanine aminotransferase (ALT) or creatinine levels in mice administered high amounts of 111In-DTPA-hEGF (equivalent to human doses up to 14,208 MBq) and by light and electron microscopy of the tissues. RESULTS: Approximately 70% of 111In-DTPA-hEGF was internalized by MDA-MB-468 cells within 15 min at 37 degrees C and up to 15% was translocated to the nucleus within 24 h. Chromatin contained 10% of internalized radioactivity. The growth rate of MDA-MB-468 cells was decreased 3-fold by treatment with 111In-DTPA-hEGF (45-60 mBq/cell). Treatment with unlabeled DTPA-hEGF caused a 1.5-fold decrease in growth rate, whereas treatment with 111In-DTPA had no effect. Targeting of MDA-MB-468 cells with up to 130 mBq/cell of 111In-DTPA-hEGF resulted in a 2-logarithm decrease in their surviving fraction. No decrease in the growth rate or surviving fraction of MCF-7 cells was evident. There was no evidence of hepatotoxicity or renal toxicity in mice administered high amounts of 111In-DTPA-hEGF. Radiation dosimetry estimates suggest that the radiation dose to an MDA-MB-468 cell targeted with 111In-DTPA-hEGF could be as high as 25 Gy with up to 19 Gy delivered to the cell nucleus. CONCLUSION: 111In-DTPA-hEGF is a promising novel radiopharmaceutical for targeted Auger electron radiotherapy of advanced, hormone-resistant breast cancer.

Factors influencing the sensitivity of tumor imaging with a receptor-binding radiopharmaceutical.

UNLABELLED: The overexpression of cell surface receptors on cancer cells is a potential target for the design of receptor-binding radiopharmaceuticals for tumor imaging. The sensitivity of these agents depends on the interaction in vivo of factors such as the level and heterogeneity of receptor expression, the proportion of targeted cells, the tumor/ nontarget (T/NT) ratio and attenuation by overlying normal tissue. The relative importance of a single factor or combination of factors is unknown. Our objective was to evaluate, under controlled experimental conditions, the effect of these factors on the sensitivity for imaging breast cancer with a new receptor-binding radiopharmaceutical: human epidermal growth factor (HEGF)51 labeled with 111In. METHODS: MDA-MB-468, S1 or MCF-7 breast cancer cells expressing 1.3 x 10(6), 3.3 x 10(4) and 1.5 x 10(4) epidermal growth factor receptors (EGFR)/cell were targeted in vitro with 111In-HEGF51. Phantoms were constructed with an internal well to simulate a lesion and surrounded by an outer well to simulate normal tissue. The effect of the level of receptor expression was studied with phantoms containing targeted MDA-MB-468, S1 or MCF-7 cells. The effect of the proportion of cells targeted was evaluated using phantoms containing mixed targeted or nontargeted MDA-MB-468 cells. Receptor heterogeneity was studied using phantoms containing mixed MDA-MB-468 and S1 cells. The T/NT ratio was evaluated by varying the concentration of radioactivity in the outer well and tissue attenuation was simulated by overlaying the phantoms with water. Phantoms were imaged using a gamma camera fitted with a medium-energy collimator interfaced to a computer. RESULTS: The sensitivity for detection of a lesion was directly proportional to the level of receptor expression or to the proportion of cells targeted and inversely proportional to the level of receptor heterogeneity. A T/NT ratio > or = 2:1 was required for detection. Under ideal conditions with a single factor varied, as few as 5 x 10(4) to 10(5) MDA-MB-468 cells with a high level of EGFR expression or 2.5 x 10(5) to 10(6) S1 or MCF-7 cells with a low level of EGFR expression were detected. When the receptor heterogeneity, the proportion of targeted cells and tissue attenuation were varied in combination with a T/NT ratio of 3:1, the sensitivity for detection approached that observed clinically with receptor-binding radiopharmaceuticals (10(7) cells). CONCLUSION: Our results suggest that combinations of four factors may account for the relatively low sensitivity for tumor imaging observed clinically with receptor-binding radiopharmaceuticals and, in particular, strategies aimed at minimizing the effects of receptor heterogeneity; a low proportion of cells targeted and tissue attenuation would improve the detection of small lesions.

Pre-operative assessment of axillary lymph node status in patients with breast adenocarcinoma using intravenous 99mtechnetium mAb-170H.82 (Tru-Scint AD).

Immunoscintigraphy of the axilla has potential utility for the diagnostic and prognostic assessment of patients with breast adenocarcinoma. mAb-170H.82 is a murine monoclonal antibody (mAb) derived against synthetic Thomsen-Friedenreich (TF) antigen. Tru-Scint AD, a 99mTc-mAb-170H.82 immunoconjugate, has previously been shown to localize in various human adenocarcinomas. The purpose of this study was to evaluate the accuracy of this immunoconjugate in the pre-operative assessment of axillary lymph nodes in patients with known breast adenocarcinoma. Sixteen patients with documented primary breast cancer were injected intravenously with 1 mg of immunoconjugate (radioactivity 1.8 GBq) and imaged 22-24 hrs post-injection. Both planar and single photon emission computed tomographic (SPECT) images were obtained and reviewed in a blinded fashion. Imaging results were compared with surgical and pathological findings. Seven of 16 patients were found to have histologically positive axillary nodes: 5 of these sites were detected by immunoscintigraphy (sensitivity = 71%). Nine patients had pathologically disease-free axillary nodes: only 1 of these was misidentified as positive by immunoscintigraphy (specificity = 89%). These results suggest that immunoscintigraphy with 99mTc-mAb-170H.82 has promise in the detection of axillary lymph node involvement in patients with breast cancer. Further studies are warranted to define the role of immunoscintigraphy in axillary staging.

Oral delivery of antibodies. Future pharmacokinetic trends.

Antibodies have been investigated as specific targeting agents for cancer diagnosis and therapy, to inactivate toxic substances including drugs and also as passive immunotherapy for neoplastic or infectious diseases. In most cases the antibodies were administered systemically by the intravenous route. More recently, however, there has been increasing interest in the oral administration of antibodies for localised treatment of infections or other conditions in the gastrointestinal tract. The normal physiological handling of ingested proteins is degradation by proteases in the stomach and intestine into small peptides or amino acids which are subsequently absorbed. Proteolytic enzymes involved in the degradation of orally administered immunoglobulins include pepsin, trypsin, chymotrypsin, carboxypeptidase and elastase. These enzymes initially degrade the antibodies to F(ab')2. Fab and Fc fragments. The F(ab')2 and Fab fragments, however, retain some of their neutralising activity locally in the gastrointestinal tract. Various approaches are possible to increase the stability of orally administered antibodies against proteolysis, including formulation in liposomes, coating with polymers and genetic engineering of resistant forms. The clinical application of orally administered antibodies includes the treatment and prevention of gastrointestinal infections caused by enteric pathogens such as rotavirus, Escherichia coli or Vibrio cholerae in susceptible individuals including those with immunodeficiency diseases and patients with bone marrow transplants. There is also a suggestion that such agents may be useful in preventing chemotherapy-induced gastrointestinal mucositis. Future opportunities for research include the design of oral dosage forms of antibodies which resist proteolysis and can deliver a greater fraction of immunoreactive antibody locally in the gastrointestinal tract for the treatment of infections or perhaps even to allow the absorption of antibodies for the treatment or prevention of systemic conditions.

Pretargeted tumour imaging with streptavidin immunoconjugates of monoclonal antibody CC49 and 111In-DTPA-biocytin.

Pretargeted tumour imaging was performed in nude mice bearing subcutaneous LS174T human colon cancer xenografts with streptavidin-CC49 monoclonal antibody and 111In-DTPA-biocytin. Mice were administered 250 micrograms of streptavidin-CC49, followed 6 or 9 days later by 40 ng (250 microCi) of 111In-DTPA-biocytin. Tumors were visualized at 24 h postinjection of 111In-DTPA-biocytin. Tumour uptake was 0.9-2.5% injected dose/g with tumour/nontarget ratios from 2:1 to 37:1 (except for kidney, which was 0.5-3:1). Tumour uptake in mice pretargeted with streptavidin or streptavidin-conjugated nonspecific normal mouse IgG was < 0.1% i.d./g.

A new radioligand for the epidermal growth factor receptor: 111In labeled human epidermal growth factor derivatized with a bifunctional metal-chelating peptide.

More specific radiopharmaceuticals are currently being evaluated for the in vivo detection and therapy of breast cancer. The human epidermal growth factor (hEGF) represents a good radiopharmaceutical candidate in view of the reported overexpression of its receptor by breast cancer cells. To enhance the imaging potential of this peptide ligand, a synthetic strategy was developed to rapidly create small peptides containing a large number of metal-chelating groups that can be readily coupled to hEGF. A prototypic 15-amino acid branched peptide containing four EDTA-like chelator groups was assembled by solid phase peptide synthesis. The metal chelating peptide, abbreviated MCP-4-EDTA-SH, was selectively incorporated into hEGF(1-51) at its unique N-terminus amino group. The coupling of a single MCP-4-EDTA-SH into hEGF(1-51) was confirmed by SDS polyacrylamide gel electrophoresis, western blotting, and amino acid analysis. The protein conjugate was successfully labeled with 111In. Its specific binding to EGF receptors present on MDA-MB-468 breast cancer cells confirmed that such a construct retains the properties of the natural ligand.

A novel anti-seminoma monoclonal antibody (M2A) labelled with technetium-99m: potential application for radioimmunoscintigraphy.

OBJECTIVE: To study the potential usefulness of monoclonal antibody (mAb) M2A specific for seminoma to image tumour nodules in a preclinical nude mouse model. MATERIALS AND METHODS: MAb M2A was labelled with technetium-99m (99mTc) following reduction and was administered intraperitoneally to nude mice bearing subcutaneous HEY cell xenografts against which the antibody was originally raised. Biodistribution and gamma scintigraphy studies were performed 24 h after administration of 99mTc-M2A. RESULTS: Biodistribution studies showed specific targeting of 99mTc-M2A to HEY tumours in comparison with control mAb 99mTc-6E8 and 99mTc-2G3 which do not bind to HEY cells. Subcutaneous HEY cell tumours (0.5-1.0 g) were successfully imaged using gamma-scintigraphy following administration of 99mTc-M2A. CONCLUSION: The results of this study indicate the potential usefulness of 99mTc-M2A as a clinical reagent for imaging seminoma metastases.

Problems of delivery of monoclonal antibodies. Pharmaceutical and pharmacokinetic solutions.

Monoclonal antibodies to tumour-associated antigens have great theoretical potential for the specific targeting of radioactivity and anti-neoplastic agents to tumours. The clinical success of monoclonal antibody-based cancer diagnosis and therapy depends, however, on solving a number of pharmacokinetic delivery problems. These include: (i) slow elimination of monoclonal antibodies from the blood and poor vascular permeability; (ii) low and heterogeneous tumour uptake; (iii) cross-reactivity with normal tissues; (iv) metabolism of monoclonal antibody conjugates; and (v) immunogenicity of murine forms in humans. As a result of extensive pharmaceutical and pharmacokinetic research conducted over the past 10 to 15 years, several potential solutions to these delivery problems have been identified. Blood concentrations of antibody conjugates may be reduced through regional administration, the use of antibody fragments, interventional strategies and various pre-targeting techniques. Tumour uptake may be increased through administration of higher doses, or the use of agents to increase tumour vascular permeability. Tumour retention of antibody conjugates may be improved by inhibition of metabolism, by using more stable linkage chemistry. Alternatively, normal tissue retention may be decreased through the use of metabolisable chemical linkages inserted between the antibody and conjugated moiety. Very small antigen-binding fragments and peptides that exhibit improved tumour penetration and more rapid elimination from the blood and normal tissues have been prepared by genetic engineering techniques. Chimeric (mouse/human) and human monoclonal antibodies have been developed to circumvent the problem of immunogenicity. Future research will continue to be focused on improvements in the design of monoclonal antibodies for tumour targeting, with the ultimate goal of finally uncovering the 'magic bullet' envisioned by Paul Ehrlich almost a century ago.

In vitro and in vivo evaluation of streptavidin immunoconjugates of the second generation TAG-72 monoclonal antibody CC49.

Streptavidin was conjugated to the second-generation TAG-72 monoclonal antibody CC49 at lysine amino acids, oxidized carbohydrates or reduced disulfides on the immunoglobulin. The streptavidin immunoconjugates were radiolabelled with 111In-DTPA-biocytin and their immunological characteristics evaluated in vitro and in vivo. FPLC analysis showed a single peak (mol. wt > 350 kDa) for the lysine conjugate and sulfhydryl conjugate (mol. wt approximately 210 kDa) but multiple peaks (approximately 210 to > 350 kDa) for the carbohydrate conjugate. There were only small differences in immunoreactivity against bovine submaxillary mucin in vitro. However, in mice bearing subcutaneous LS174T tumours, the lysine conjugate exhibited significantly lower tumour uptake (< 2% i.d./g) compared to the other streptavidin-CC49 conjugates (10-40% i.d./g) or DTPA-CC49 (14-18% i.d./g). Due to the monomeric nature and smaller molecular size of the sulphhydryl conjugate, and its similar in vitro and in vivo characteristics compared with DTPA-CC49, this conjugate has been selected for future pretargeting studies with 111In and 90Y biotin.

Mapping effector functions of a monoclonal antibody to GD3 by characterization of a mouse-human chimeric antibody.

R24, a mouse monoclonal antibody against GD3 ganglioside, exhibits a wide range of in vitro effector functions. It also has the ability to bind to itself, presumably through homophilic Fab-Fab interactions, which have been proposed to contribute to its high relative avidity for GD3 and to its effector function activity. It is not known which of these characteristics is necessary for the antitumor effects observed in melanoma patients treated with R24. A mouse-human chimeric R24 (chR24) molecule has been constructed in which the GD3-binding site is preserved. Chimeric R24 demonstrates a lower level of binding to GD3 than does mouse R24 suggesting that there may be some differences between the GD3-binding sites of the two mAb or that Fc determinants can contribute to R24 avidity for GD3. The property of homophilic binding is retained by chR24, demonstrating formally that homophilic binding of R24 involves interactions between variable domains. Both R24 and chR24 fix human complement and mediate antibody-dependent cellular cytotoxicity although chR24 was slightly less efficient at the latter. Unlike R24, chR24 was not able to inhibit melanoma cell attachment to plastic surfaces and was not able to activate human T lymphocytes. We hypothesize that chR24 does not bind to GD3 with an avidity high enough to mediate these effector functions.